The present invention relates generally to gas turbine engines, and, more specifically, to exhaust nozzles in turbofan aircraft engines.
In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases from which energy is extracted in turbine stages. A high pressure turbine (HPT) follows the combustor and extracts energy from the combustion gases for powering the compressor. A low pressure turbine (LPT) follows the HPT and extracts additional energy from the gases for powering an upstream fan in an exemplary turbofan aircraft engine application.
Modern turbofan aircraft engines have undergone decades of continuing development for maximizing aerodynamic efficiency while minimizing weight thereof, and for also achieving long useful life. Engine efficiency may be simply evaluated by specific fuel consumption (SFC) in which fractionally small improvements thereof are significant in reducing fuel consumption of the engine when powering the aircraft in flight.
The typical turbofan engine includes an annular fan nozzle which discharges the pressurized fan air for producing a majority of the propulsion thrust. A core nozzle follows the fan nozzle and discharges the spent combustion gases which add to the propulsion thrust.
The aerodynamic design of the fan and core nozzles is also subject to continuing development for further increasing aerodynamic efficiency thereof, including corresponding thrust coefficients.
The typical exhaust nozzle includes an annular outlet duct that converges to a throat of minimum flow area, which throat affects performance of the upstream components. The exhaust nozzles are typically axisymmetrical about the longitudinal or axial centerline axis of the engine for maximizing performance and efficiency under conventional design practices.
However, the aircraft engine must be suitably mounted in the aircraft and this is typically accomplished by a supporting pylon that provides a frame to which the engine is rigidly attached.
The typical wing pylon supports the engine vertically under the aircraft wing with the pylon occupying the twelve o'clock circumferential position of the engine.
The fan nacelle is typically formed in two circumferential halves typically referred to as C-ducts for allowing the nacelle to be opened in clamshell fashion for accessing the core engine during maintenance outages. In this configuration of the turbofan engine, a lower bifurcation or longitudinal beam is located at the bottom or six o'clock position of the engine.
Accordingly, the upper pylon and lower beam typically interrupt the circumferential continuity of the annular fan duct and the fan nozzle. The fan exhaust is therefore discharged from the fan nozzle in two discrete C-duct portions for collectively providing propulsion thrust.
However, the introduction of the upper and lower bifurcations correspondingly affects the circumferential continuity of the velocity and pressure distributions of the pressurized fan air which correspondingly reduces aerodynamic performance and efficiency of the nozzle.
Accordingly, it is desired to provide an exhaust nozzle having improved efficiency notwithstanding circumferential interruptions thereof.